Pediatric Audiology Conference Bridges Genetics and Clinical Practice The fast-changing field of genetics and its impact on the assessment and management of infants with hearing loss and their families was the focus of the annual Pediatric Audiology Conference, which drew over 60 audiologists to Walt Disney World Resort in Orlando, FL. The small-scale conference on Feb. 14–15 put ... Features
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Features  |   March 01, 2004
Pediatric Audiology Conference Bridges Genetics and Clinical Practice
Author Notes
  • Susan Boswell, an assistant managing editor of The ASHA Leader, can be reached at sboswell@asha.org.
    Susan Boswell, an assistant managing editor of The ASHA Leader, can be reached at sboswell@asha.org.×
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Hearing Disorders / Special Populations / Genetic & Congenital Disorders / ASHA News & Member Stories / Features
Features   |   March 01, 2004
Pediatric Audiology Conference Bridges Genetics and Clinical Practice
The ASHA Leader, March 2004, Vol. 9, 1-10. doi:10.1044/leader.FTR6.09062004.1
The ASHA Leader, March 2004, Vol. 9, 1-10. doi:10.1044/leader.FTR6.09062004.1
The fast-changing field of genetics and its impact on the assessment and management of infants with hearing loss and their families was the focus of the annual Pediatric Audiology Conference, which drew over 60 audiologists to Walt Disney World Resort in Orlando, FL.
The small-scale conference on Feb. 14–15 put participants on a first-name basis with each other and with an interdisciplinary faculty of top experts in the fields of neuro-otology, genetics, molecular biology, psychiatry, and pediatric audiology. Together, they delved into the latest research that is reshaping our knowledge of the genes responsible for hearing loss, availability of genetic tests, and ways to counsel families about genetics. Participants also learned about cutting-edge protocols for assessing the function of the auditory pathway, performing behavioral assessments and fitting amplification for the youngest infants now being identified at birth.
“The small size of the meeting made it feel intimate, and it was easy to hear and see the presentations and speakers,” said Flora Holderbaum, a pediatric audiologist in the Pediatric Resource Center at Bellevue Hospital Center in NY. “Each day was organized differently-it was an exceptionally well-organized conference.”
Role of Connexins
“When I first started, I didn’t believe that genetics played a large role in hearing loss, but I’ve come to believe that there is a genetic component to almost all cases of hearing loss,” said Linda Hood, a professor at the Kresge Hearing Research Laboratory at Louisiana State University Health Sciences Center. She presented with Andrew Griffith, acting chief, Hearing Section of the Neuro-otology branch of the National Institute on Deafness and Other Communication Disorders, on “Connexins in Deafness: Clinical Implications.”
A genetic etiology should be considered for every patient with hearing loss, but “there doesn’t necessarily need to be a family history of hearing loss for the loss to be genetic,” Hood said. “Many hereditary hearing losses are not present at birth, and the majority of hearing loss is non-syndromic in nature.”
One common mutation illustrates the difficulty involved in identifying a genetic cause of hearing loss. A mutation on a chromosome that codes for a gap junction protein (GJB2) called Connexin 26 accounts for 40%-50% of non-syndromic, prelingual hearing loss in some populations. This mutation is thought to disrupt the flow of potassium between plasma membrane channels. The resulting hearing loss is symmetrical with a flat or descending audiogram, but can produce a hearing loss that can be mild, moderate, severe, or profound.
Knowing the family heritage is critical, as common Connexin 26 (GJB2) mutations include 35delG in those who are Caucasian/European; 167delT in Ashkenazi Jews; and 235delC in East Asians, according to Griffith. Other common Connexin genes involved in hearing loss include Connexin 30 (GJB6), which causes recessive hearing loss, and there is a weak link between hearing loss and to Connexin 31 (GJB3) and Connexin 43 (GJA1).
As an audiologist, it’s important to do careful phenotyping and draw a pedigree, Hood suggested. “Take a careful family history looking at all of the relatives. Any information that we can gather will help the geneticist.”
Testing and Counseling
Testing for Connexin 26-a small gene-should be at the top of the list for genetic testing because it is a widely available, high-yield diagnostic evaluation for children with hearing loss that have no identifiable syndrome, environmental cause, or family history, said Griffith.
In “Genetic Testing and Counseling,” Heidi Rehm, associate director of the Harvard Medical School Center for Hereditary Deafness; Jill Elfenbein, associate professor at Michigan State University; and Annie Steinberg, a psychiatrist at the University of Pennsylvania School of Medicine, proposed a protocol for genetic testing and counseling, and explored the complex considerations surrounding families’ decisions to seek genetic testing and counseling.
While genetic tests are available for many types of syndromic hearing loss, only 11 clinical tests exist for non-syndromic sensorineural hearing loss. A Genetic Hearing Loss Search Engine being developed at Harvard Medical School will provide the latest information on genes involved with hearing loss, including which to consider for testing.
Prior to genetic testing, families should be referred to genetic counselor who can help families decide whether to proceed with genetic testing, and provide information about genetic hearing loss, the benefits and risks of genetic testing, as well as an interpretation of the test results.
“The path to genetic counseling is not one that parents seek themselves,” Elfenbein said. “We need to respect the decisions families make, while ensuring that they have the information to make decisions.”
Assessing and Fitting Infants
While genetics holds an important clue to the cause of the hearing loss, it’s also important to understand the nature and physiology of the hearing loss, said Linda Hood, who presented on “Audiologic Assessment of Infants” with Judith Gravel, a professor at Hunter College and the City University of New York.
Hood advocated for a “triage” of physiologic measures to assess the status of the auditory pathway, including the middle-ear and cochlear status and neural function from the peripheral through the central auditory pathway. By using a battery of assessments that include tympanograms, ipsilateral and contralateral middle-ear muscle reflexes (MEMRs), and OAEs, it is possible to estimate the hearing sensitivity and determine the location of the dysfunction along the auditory pathway.
“While OAEs and ABRs are not hearing tests,” Hood cautioned, “this is a start at predicting behavioral thresholds.” In studying the relationship between ABR tone-burst thresholds and behavioral pure-tone thresholds, a meta-analysis showed a 10 dB difference at higher frequencies and a 20 dB difference at lower frequencies for those with normal hearing. Auditory Steady-State Potentials (ASSR) also showed agreement with behavioral thresholds within 10 dB-20 dB, with better agreement with more severe hearing loss.
Physiological tests are important, but behavioral tests are crucial, Gravel emphasized. “When doing a behavioral test, it is critical to systematically follow a protocol,” Gravel said. “We’re trying to establish a recognized standard as pediatric audiologists.”
Gravel reviewed various behavioral audiometry procedures and suggested a “Test Battery Assessment Approach” which incorporates an age-based protocol that includes an in-depth case history, evoked OAEs, MEMR, ABR, and tympanometry from birth to age 4. From birth to 4 months, these tests should be supplemented with observation audiometry to serve as a cross check and determine auditory function. At 5-6 months to 24 months, ear-specific visual reinforcement audiometry should replace observation audiometry. At 24 months, ear-specific play audiometry should be used.
During a presentation on “Amplification Issues for Infants,” Jeffrey Simmons, a senior clinical audiologist at Boys Town National Research Hospital, commented that “we’ve come a long way, baby,” in just five years. A 2001 survey by Tharpe showed that 50% of pediatric audiologists now use the Desired Sensation Level (DSL) approach to fitting children, compared to a 1996 survey by Hedley-Williams which showed that more than half did not use a data-driven approach to fitting amplification.
Simmons suggested a five-step protocol for infants that include: 1) assessment and referrals for medical and genetic evaluations and early intervention; 2) selection of devices; 3) a fitting and orientation that addresses parents’ concerns; 4) verification using real-ear to coupler difference; and 5) validation using functional assessment tools to determine audibility in real-world listening situations.
Simmons also provided fitting suggestions related to specific genetic conditions, including Treacher Collins syndrome and Occulo-Auriculo-Vertebral spectrum/Goldenhar’s syndrome which may pose challenges in hearing aid retention and require a bone-conduction hearing aid. Connexin 26 mutation results in a severe-to-profound hearing loss in 60% of cases and requires a hearing aid with flexible parameters and consideration of a cochlear implant. Families of children with Usher syndrome type I should be counseled about cochlear implants, manual communication, and vestibular problems.
Children with auditory neuropathy, which accounts for 2% of all recessive hearing loss, frequently receive limited benefit from hearing aids, and cochlear implantation is not always successful. “We should be counseling these families to use visual language because these children can’t learn through audition alone,” Simmons said.
The 2004 Pediatric Audiology and Genetic Conference was dedicated to the memory of the late Michael Wynne, whose leadership and vision were critical to gaining support for the conference. Wynne was chair of ASHA’s Scientific and Professional Education Board.
The conference was supported in part by the contributions of Division 9, Hearing and Hearing Disorders in Childhood.
If you’ve missed this year’s conference, watch The ASHA Leader and the Audiology Conference section of the web site for more details on next year’s conference.
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March 2004
Volume 9, Issue 6